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doc: add compression level guide for ISA-L

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This expands the ISA-L documentation to give more a detailed explanation
of the mapping between the compressdev API levels and PMD levels.

Signed-off-by: Lee Daly <lee.daly@intel.com>
Acked-by: Marko Kovacevic <marko.kovacevic@intel.com>
This commit is contained in:
Lee Daly 2018-05-24 12:04:49 +01:00 committed by Thomas Monjalon
parent 006bb2cc20
commit 8a38e97238
1 changed files with 57 additions and 8 deletions
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65
doc/guides/compressdevs/isal.rst
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@ -6,7 +6,8 @@ ISA-L Compression Poll Mode Driver
The ISA-L PMD (**librte_pmd_isal_comp**) provides poll mode compression &
decompression driver support for utilizing Intel ISA-L library,
which implements the deflate algorithm for both compression and decompression
which implements the deflate algorithm for both Deflate(compression) and Inflate(decompression).
Features
--------
@ -15,25 +16,73 @@ ISA-L PMD has support for:
Compression/Decompression algorithm:
* DEFLATE
* DEFLATE
Huffman code type:
* FIXED
* DYNAMIC
* FIXED
* DYNAMIC
Window size support:
* 32K
* 32K
Level guide:
The ISA-L levels have been mapped to somewhat correspond to the same ZLIB level,
i.e. ZLIB L1 gives a compression ratio similar to ISA-L L1.
Compressdev level 0 enables "No Compression", which passes the uncompressed
data to the output buffer, plus deflate headers.
The ISA-L library does not support this, therefore compressdev level 0 is not supported.
The compressdev API has 10 levels, 0-9. ISA-L has 4 levels of compression, 0-3.
As a result the level mappings from the API to the PMD are shown below.
.. _table_ISA-L_compression_levels:
.. table:: Level mapping from Compressdev to ISA-L PMD.
+-------------+----------------------------------------------+-----------------------------------------------+
| Compressdev | PMD Functionality | Internal ISA-L |
| API Level | | Level |
+=============+==============================================+===============================================+
| 0 | No compression, Not Supported | --- |
+-------------+----------------------------------------------+-----------------------------------------------+
| 1 | Dynamic (Fast compression) | 1 |
+-------------+----------------------------------------------+-----------------------------------------------+
| 2 | Dynamic | 2 |
| | (Higher compression ratio) | |
+-------------+----------------------------------------------+-----------------------------------------------+
| 3 | Dynamic | 3 |
| | (Best compression ratio) | (Level 2 if |
| | | no AVX512/AVX2) |
+-------------+----------------------------------------------+-----------------------------------------------+
| 4 | Dynamic (Best compression ratio) | Same as above |
+-------------+----------------------------------------------+-----------------------------------------------+
| 5 | Dynamic (Best compression ratio) | Same as above |
+-------------+----------------------------------------------+-----------------------------------------------+
| 6 | Dynamic (Best compression ratio) | Same as above |
+-------------+----------------------------------------------+-----------------------------------------------+
| 7 | Dynamic (Best compression ratio) | Same as above |
+-------------+----------------------------------------------+-----------------------------------------------+
| 8 | Dynamic (Best compression ratio) | Same as above |
+-------------+----------------------------------------------+-----------------------------------------------+
| 9 | Dynamic (Best compression ratio) | Same as above |
+-------------+----------------------------------------------+-----------------------------------------------+
.. Note::
The above table only shows mapping when API calls for dynamic compression.
For fixed compression, regardless of API level, internally ISA-L level 0 is always used.
Limitations
-----------
* Chained mbufs are not supported, for future release.
* Chained mbufs will not be supported until a future release, meaning max data size being passed to PMD through a single mbuf is 64K - 1. If data is larger than this it will need to be split up and sent as multiple operations.
* Compressdev level 0, no compression, is not supported. ISA-L level 0 used for fixed huffman codes.
* Compressdev level 0, no compression, is not supported.
* Checksums are not supported, for future release.
* Checksums will not be supported until future release.
Installation
------------